Radiocondenser



Patented Nov. 26, 1929` LUDWIG A. BRAND, F SIOUXICITY, IOWA.

RADIO CONDENSER -Application led March 9, 19,29. Serial No. 345,691.

invention relates to variable, electrical condensers of the type used in radio receiving outfits and has for its primary object to provide a. condenser which does not have dead end losses. Y

Another object of my invention is to provide a condenser wherein the inductive capacity may be changed through veryminute variations and wherein the capacity may be reduced at one end of the scale to a minimum. lMore particularly my invention refers to that type of condenser employing the helical screw type plate, one plate screwing into the other. In this type of condenser, the minimum capacity may be brought to' a very small figure, owing to the fact that the condenser may be constructed with only two plates, one a xed and the other a movable plate and these may be" so rotated that at the beginning oftheirvoverlapping engagement only two' edges aref'lgought into proximity, whereas in the ordinary ...condenser of the movable, parallel plate type, theredges of,a

.l plurality of plates approach eaih other si' y multaneously as the condenser is\turnedv toward full ca acity pgls'itionz Anotheo ject/o'f'my inventionis to ro.- vide a condenser of the screwtype, in w ch there will be no dead end losses, whereas in the ordinary condenser of the'parailellplam type, VVthere are as many loose ends asV there are plates.

Further advantages of the screw type condenser are as follows: Whereas a parallel plate condenser ofeleven plates-or more has 97 wave lengths in four inches of circumference, the screw type condenserl has 97wave lengths in 56 inches of circumference and :consequently the wavelengths are fourteen times farther apart on the screw; type con,- denser than they. are on the parallel plate type. For instance, the condenser, having six turns on each helical plate,theitotal cirf cumference of all of the tnrns is approxi-` mately 56 inches and as the movable plate is rotated six times between its two' extreme positions of complete disengagement and complete engagement, the distance that it is rotated to shift from one wave length to anotherwill be fourteen times asgreat as the distance that the parallel plate condenser referred to above is rotated to vary the capacity in the same amount.

Further advantages, of the screw plate condenser reside in the fact that only fifteen pieces are required to construct it whereas in an 11 plate condenser, over 7 5 separate pieces are required.

In further referencetto the elimination of dead end losses the ordinary 1l plate condenser has 11 loose load ends whereas a helical condenser has none. l i

A number of Vproblems are presented in a condenser of the screw plate type. first place, it is a diiiicult matter to form the In the plates so that they will retin accurately 4the 'contemplates a structure in kwhich it is not entirely essential that the plateslbe given a permanent accurate form.-

Itis my purpose in answering this problem to provide means for mounting the plates, which is also adapted to retain them permanently in their properly Aspaced relal tion' and to positively prevent contactvbe tween the, plates without interfering with the .rotation of the plates relative to each-V other on.theelectrical oscillation of the plates.v

'Withtlxe'se `and other objectsfin view, my invention consists in the construction, ar# rangement andcombination of the various parts of my device, whereby the objects contemplated are attained, as hereinafter more fully -set forth, pointed out in my claims, and illustrated inthe accompanying drawings, in

The figure shows a longitudinal', sectional view .through the condenser embodying my invention.A fr

In carrying out my invention, I provide a shell 10, insulating material such as bakelite, hard rubber composition or the like, which is cylindrical in form. The shell 1 may be secured to the panel -2 of a ,radio set by means of' a support bracket or collar 3 secured tothe shell and adapted to be secured to the shell and adapted to be secured to the panel 2.

The shell is provided with an end wall il, which may be secured in any manner such as by the collar 5.

The lined condenser plate ti is supported by the shell with its outer edge connected thereto in some manner such as by imbedding in the materialof the shellas shown. llrelplate 6 is of helical form, beingperpendicular to 'ts axis along a radial, cross-sectional out. The inner edge of the plate is spaced radially from the axis of the helix to form an axial opening. Y.

The variable plate 7 is mounted on a sleeve 8, which in turn is mounted on a shaft 9 of conductive material. rlhe sleeve 8 is of nonconductive material similar to that of the shell 1. The preferable manner of securing the plate 7 to the sleeve 8 is by imbedding its inner edge in the sleeve as shown. |The plate 7 is of identical, helical shape, pitch, etc., with the plate 6 and is adapted to be threaded into the space between the convolutions of the plate 6 and to be spaced equidistantly at all points at adjacent convolutions thereof.

In order to space the outer edge 'ofthe variable plate from. the outer edge of the fixed plate and to .positively insulate saidouter edges from each othery the shell 1 is provided with an interiorrhelical groove 10, in which the outer edge bf the variable plate is kreceived. The groovelO is of sufficient width to all-ow -the'variable plate to move readily in a circumferential direction Within the groove and is spaced equidistantly from the ixed.

plate convolutions so as to enforce the positioning of the variable plate convolutions substantially midway between of the Xed plate.

lnthe same'manner, in order to .positively insulate.: :the inner edge of the iixed plate from 'the inner edge of the variable plate, the sleeve 8 is provided with alielical groove 11, in which the inner edge of the fixed plate is received. rlibe groove 11 is positioned midway between the convolutions of the variable plate."-v v l a rlhe sleeve 8 is slidably but non-rotatably mounted on the squared portion 12 of the shaft 9 sovthat it may'slide longitudinally of the shaft and yet be given rotative movement when the shaft'is rotated.

lt will now be seenfthat the groove conthe convolutions struction serves three functions; namely:

1. As the shaft 9 is rotated by means of the dial knob 13 or the like, the variable plate will be fed forwardly as its outer edge threads its way forwardly in the groove 10. in this connectiom' it may be notedthatin other condensers of thefhelical plate type7 it has been found necessary'to employ. a threaded feed rod, generally formed as an extension of the shaft and athreadedsleeve or nut, into which said rod is threaded. the thi-mds on the feed rod being *tched to correspond with the pitch of the fiable plate,a therebymaintain- .grooves provide ridges or threads of insulating material separating the plates and'insulating them from each other. These threads are not of suiicient depth to materially out down. the size of the air dielectric.

lt will be understood that the drawinghas been .exaggeratedl somewhat for the'sake of clearness and .that the amount of` spacing shown between the plates and the sides of the grooves in which they are received is somewhat larger than is contemplated in the manufacture of `the structure' 'of my invention. Sufficient spacing betweenthe plates and the sides of the grooves is provided in order that friction may be reduced tol a minimum. It will be understood that some variation mightr be made in the amount of spacing without departing from the real spirit of my invention.

' The fixed plate is connectedas. at 14 to a -'suitable terminal 15. rlhe variable plate-7 is connected as at 16 to the collar 17, which is of conducting material and adapted to be secured to the shaft 12 by means of asetnscrew 18 in any of several adjusted ositions. The collar 17 thus servesthe dou le function of., acting as an electrical lconnection to secure the wire 16 to the shaft 12 and to 'act as a stop to limit the .unthreading `movement of the collar 8.

' in this connection, it may be .noted that in many cases the lower limit of capacity desired for the condenseris a very ,substantial amount andl there is no necessity for reducy ing 'the capacity beyond this amount` Therefore it will be. desirable to limit the unthreading of the movable plate from the fixed plate at the point where this lower limit of capacity is obtained. y

. The shaft 12 is connected to a terminal 19.

Vby'means of a bushing 20 of conducting material in which one end of the'sliaft is journalled.

As the plates are' threaded together, the c apacity commences .between the engaging ei:- tremities and -is gradually increased as more convolutions are inter-engaged.

There are no 'dead end losses because the terminals 15 and 17 are connected to the remote extremities of the plates and no portion of either plate is ever .cut out of. the circuit.

cdome changes .may be made in the constructif and ougmnent of Lhe parts of Yinvention. rom 'the real ietf mamon 3 l shell of insulating material, provided With internal helical grooves, a xed plate of helical form, mounted With its outer edge embedded in the shell, a shaft of conductinof material journalled at the axis of the shell, .a varia-ble plate of helical form mounted on the ment, and an electrical connection shaft and threaded intothe helical groove of the shell, a brush against which the shaft contacts during its sliding and rotatin moveetween the shaft andthe variable plate at the end of tlie'latter remote from the fixedplate, the

axis ofthe shell, and a variable plate of helishafty being insulated from the variable plate durinff the remainder of its length.

2. n a variable condenser7 a cylindrical shell of insulating material, provided with internal helical grooves, a fixed plate of h elicalv form, mounted With its outer edge embedded in the shell, a Shaft journalled at the cal form mounted on the shaft and` threaded into the helical groove of the shell, the shaft being insulated from the-'variable plate during the remainder of its length 3. In av variable condenser, a cylindrical shell ofi'nsulating material, provided with internal helical grooves, a ixed plate ofhelical form, mounted. with its outer edge supj ported by the shell, a shaft journalled at the axis ofthe shell, and a variable ,plate of helical form mounted on the shaft and threaded into the helical groove of the shell,- the shaft being insulated from the variable plate during the remainder of its length.

4. In a variable condenser, a cylindrical shell of insulating material, a fixed plate of helical form, supported at its outer edge by the shell open at its axis, a shaft journalled at the axis of' the shell, a sleeve of insulating 'material mounted on the shaft, a variable plate mounted on the sleeve, the sleeve being provided with a helical groove, into which the inner edges of the iixed plate is threaded.

5. In a variable'condenser, a cylindrical shellof insulating material, a fixed plate of helical form, supported at its outer edge by the shell open at its axis, a shaft journalled at the axis of the shell, a sleeve of insulating material mounted on the shaft, a variable plate Vmounted on the sleeve, the sleeve being provided with a helical groove, into which the inner vedges of the ixed plateis threaded, a brush against Which the shaft contacts during its sliding and rotating movement, and an electrical connection between the Shaft and the variable 1late at the end of the vlatter re'- shell of insulating material, a'iixed plate of helical form, supported at its outer edgeb the shell open at its axis, a shaft journalle 4at the axis of the shell, a sleeve of insulating material mounted on the shaft, a variable plate mounted on the sleeve, the inner edge of the latter plate beingembedded in the material of the sleeve, the sleevebeinjg provided with a helical groove, into which the` inner edges of the xed plate is threaded.

7. In a variable condenser, a cylindrical `shell of insulating material, a xed plate of helical form, supported at its outer edge by the shell open at its axis, a shaft journalled at the axis of the shell, a sleeve of'insulating materiai mounted on the shaft, a variable plate mounted on-the sleeve, the sleeve being provided with a helical groove, into which the inner edges of the fixed plate is threaded, and 'Y the-shell being providedv with an internal helical groove, into which the outer edge of 'the variable plate is threaded, whereby the plates are reinforced in their spaced relation, y

by insulating mediums.

Signed this 6th day of March, 1929, in the county of Woodbury and State of Iowa.

` LUDWIG A. BRAND. 

